CHAPTER II. Preliminary Remarks on Physiology and Chemistry. (Part 1)

CHAPTER II. Preliminary Remarks on Physiology and Chemistry. The study of the physiologic and chemical processes of digestion varies according to whether the point of view is that of a physician, a physiologist, or a chemist. The two latter are concerned only in the process itself, whereas a physician must draw certain conclusions from the normal proc which will aid him in the treatment of his patients. ‘The physiologist studies the organ itself, separated from the rest of the digestive tract ; but the physi cian considers the gastrie digestion as only a partial phenomenon of diges- tion, and therefore includes also the oral and intestinal digestion. 'The fol- lowing discussion will only cover the cardinal points of the processes of digestion; for a more detailed consideration of the subject, reference should be made to text-books on physiologic chemistry (Hammarsten, Bunge, Neumeister, Gamgee, and others). That digestion begins with the dividing and masticating of the morsels and with the swallowing of liquids is common knowledge. All physicians are familiar with the fact that the food in the mouth is intimately mixed with saliva (salivation), which continues its activity in the stomach with the production of important changes, and that the morsel becomes simultane- ously thinner and lubricated. We know, moreover, that carious teeth, putre- factive oral processes, and discase of the salivary glands have a decided influ- ence upon digestion, ‘These disturbances are largely due to bacteria, our Knowledge of which was greatly advaneed by the investigations of recent years. We are especially indebted to the noteworthy investigations of W. D Miller? on the bacteria of the mouth and their relation to the digestive pro- cesses, to a consideration of which we will return later. Miller found two groups of organisms in the mouth, as well as in the stomach, which produced fermentation. The one variety decomposes carbohydrates, with formation of acid substances, and the other type eauses decomposition of proteids, with formation of alkaline products. We observe either one or both varicties of fermentation, depending upon the presence or predominance of one or the other form of food. Miller has furthermore demonstrated that the action of mierobes upon the proteids led constantly to putrefactive changes, with formation of sulphuretted hydrogen, ammonia, carbonic acid, ete. and a large number of bases (ptomaincs). ‘There can be no doubt, therefore, that ‘Miller, Die Mikroorganismen der Mundhihle, 2 Auflage, Leipzig, 1892, G. Thieme. (15) 16 PHYSIOLOGY AND CHEMISTRY, a solution, or rather decomposition, of the proteids occurs under those cir- cumstances. That this process is comparable to the peptonising property of the well- known gastrie and intestinal enzymes is, however, out of the question, a fact wh was also emphasised by Miller. We have, therefore, to look upon micro-organisms which decompose the proteids as injurious to the digestive cycle and the general health of the body. ‘These investigations have consid- erably advanced our knowledge of the reciprocal relations existing between the digestive processes of the mouth and of the stomach, well-known even to the earlier physicians (see below). ‘The most important secretion of the oral cavity is the saliva, the significance of which in the digestion of food will be discussed in detail. The Saliva. ‘The saliva is a mixture of the secretions from the salivary and mucus glands, which consists of a viscid and tenacious opalescent fluid. ‘The quan- tity of saliva secreted during twenty-four hours equals, according to Bidder and Schmidt,? 1400 to 1500 grammes; according to Fr. Kriiger,* 250 to 300 grammes; according to W. G. A. Robertson,‘ 331 to 407 grammes. The re- action is strongly alkaline, provided an indicator (methyl-orange) is em- ployed which remains unaffected by CO, ; whereas the reaction is found to be decidedly acid if phenolphthalein be used, which is very sensitive to CO, (Dieminger,? M. Cohn®). According to Chittenden and Ely, the alkalinity equals a solution of 0.8 per mille Na,CO,. The degree of the alkalinity presents certain variations in the course of a day. Its specific gravity equals 1002 to 1009, usually from 1003 to 1004. The amount of solid matter equals 5 to 10 per cent., and consists of epithe- lium, mucus, ptyaline, albumen, and salts. A constituent peculiar to saliva is mucin. The analysis given in the table on page 17 (by Hammarsten) presents the average constituency of the human saliva. ‘The figures are referable to 1000 parts. The mixed saliva also contains an acid combined with potassium thiocyanate, which has not yet been isolated and which appears to be practi- cally of secondary importance. ‘This constituent may be demonstrated by acidulating the saliva with hydrochloric acid and adding, drop by drop, a ? Bidder and Schmidt, Die Verdauungssiifte und der Stoffwechsel, Mitau and Leipzig, 1852. * Fr. Kriiger, Zeitschrift fiir Biologie, 1897, Bd. 37, S. 6-24. 4 W. G. A. Robertson, Journal of Anatomy and Physiology, 1898, Bd. 32, S. 615. 5 Dieminger, Inaug-Diss., Wiirzburg, 1898. ®M. Cohn, Deutsche medicinische Wochenschrift, 1900, No. 4. SALIVA, 17 Terzetius| J@kuho | Freriehs [fMdmann| srerter | Lehmann | "Amumer- Water. 2... 992.9 | 995.16 | 904.1 | 988.3 | 9917 |... 994.2 Solid Material . . T1.| 481) 59 | 117 | 53 | 35-84 | 58 Itered Mucus and Epithe, | Saliva) lium... 14} 162) 213 wot as achat BS Soluble Organic Sub- | | stances: . 3.8 1.34 1.42 wee 3.27 was 14 Potassium Thicey mates... [es 0.06} 010 |... .] .. . |0,064—0.09, 0.04 Salts = 1.91 1.62/ 2.19 1.30 22 weak solution of the chloride of iron, which produces a dark-red or Bur- gundy-red colour (formation of ferri-thiocyanate). Or add a little hydri« odie acid to the saliva, which is reduced by means of formation of thiocya- nate and free iodine, the latter being easily detected by means of starch- paste (reaction of Solera). ‘The amount of potassium thiocyanate is fre- quently increased in cases of chronie pharyngitis and of abnormal forma- tion of mucus, also in association with vomitus matutinus, and, according to Fr. Kriiger, also with tobacco-smoking; its amount is lessened in each exia and severe diseases of long duration (Jul. Grober’). According to Schinbein’s* observation, nitrous acid is also present in the saliva. If a solution of potassium iodide in starch-paste is added to the saliva which has been acidulated with sulphuric acid, the formation of iodide starch will frequently be noted. ‘The principal action of the saliva is diastatie, which depends upon the presence of an extremely tenacious and active enzyme, called ptyaline, or bet= ter, salivary diastase, It converts all the starches, as well as glycogen, into sugar. Ptyaline acts in a slightly alkaline, neutral, or extremely slightly acid medium. It is most energetic, according to Chittenden and Smith, in neutral or even beticr in a slightly acid reaction. Ptyaline occurs not only in adults, but also in newly-born infants. Zweifel® claims that in the new-born. ptyaline is found only in the parotid and not in the submaxillary gland. It is supposed not to appear in the latter until two months after birth. Starch is converted, by means of the salivary diastase, into maltose T Jul. Grober, Deutsches Archiv fiir klinische Medicin, 1901, Bd. 69, S. 243, 8 Schénbein, Journal fiir praktische Chemie, Bd, 86, 8. 451. ® Zweifel, Untersuchungen fiber den Verdauungsapparat der Neugeborenen, Ber- lin, 1874, 2 18 PHYSIOLOGY AND CHEMISTRY, | (Dubrunfaut,? O’Sullivan,? Musculus and y. Mering,’? Brown and Heron"), or isomaltose (B. Kiilz and J. Vogel,* K. Hamburger'), and minute quantities of dextrose: The dextrose appears to be but the product of inversion of the maltose by glucase (‘Tebb, Rdhmann and Hamburger). ‘The conversion occurs more rapidly in case of cooked (starch-paste) than in raw starch, yet the saccharification of the latter, as I have discovered,” and as one may easily determine, occurs in a few minutes and is by no means slower than through action of the pancreatic diastase. The action of the saliva upon the food is almost immediate, so-that reducing substances may already be found in the mass after a few seconds. Nevertheless, several inter- mediate stages are distinguished before complete saccharification occurs. ‘These have been carefully studied by Briicke’ and may be traced as follows: 1. The diastase causes liquefaction of the starch, which, in contra- distinction to the starch-paste, is a true solution. This product, which is termed amidulin or amylodextrine, still gives a distinct blue colour when treated with a dilute solution of iodine in iodide of potassium (pure iodine 1.0, potassium iodide 2.0, aqua destillata 100.0). 2. The colour produced by the addition of the iodine solution changes gradually and becomes more violet-blue, violet, red-violet, red- or mahogany- brown. This modification of starch is designated erythrodextrine. 3. As the action of the diastase increases, the violet or brown colour gradually fades, until finally the addition of iodine shows a colourless dex- trine, which is termed achrodédertrine. While soluble starches may be precipitated by tannic acid and alcohol, the above-mentioned varieties of dex- trine are precipitated only by alcohol. Herzfeld’? claims that still another product occurs between achroddextrine and maltose, called maltodextrine, which closely resembles maltose, but which is unfermentable, according to Brown and Heron. The specific rotation of maltodextrine is represented by (a) D=174.5°, The end product of the salivary diastase is maltose or plyalose (Nasse), ©,.H1,,0,, + 1,0. © Dubrunfaut, Ann, Ch. Phys, Ser. 3, Bd. 21, 8. 178; Cit. nach Gamgee, Die physiologisehe Chemie der Verdauung, Deutsche Ausgabe, 1897, S. 35. 1 O'Sullivan, Journal of the Chemical Society, Ser. 2, Bd, 10, S. 579; Cit. nach Gamgee. # Musculus and v, Mering eitsehr. f. physiol. Chemie, 1878 u. 1879, Bd, 2. 18 Brown and Heron, Liebig’s Annalen, Bd. 199 und 204. UE. Kiilz and J. Vogel, Zeitschrift itr Biologie, 1895, Bd. 31, S. 108. 18 K, Hamburger, Pfliiger’s Archiv, 1895, Bd. 60, S. 543-697. 36 Cit. nach Hammarsten, Lehrbuch der physiol. Chemie, 4 Aufl., S. 256, ¥ Boas, Zeitschrift fiir klinische Medicin, 1900, Bd. 17, Heft 1 und 2. ¥ Briicke, Wiener akademische Sitzungberichte, April, 1872. 1 Herzfeld, Berichte der dentsch. chemischen Gesellschait, Bd. 12, S. 2120. SALIVA. 19 Maltose, when isolated, consists of white crusts, composed of fine needles which are easily soluble in water as well as in ethyl- and methyl-aleohol, but somewhat less so in the first than is dextrose. Maltose possesses the specific rotation (a) D == 150.4 (Brown and Heron), therefore almost thrice that of dextrose, (a) 52.5. Maltose possesses less reducing power for Fehling’s and similar solutions than dextrose, it being able to precipitate only tw thirds of the amount of cuprous oxide preeipitated by the latter. ‘The exact relation between them, according to Brown and Heron, is 60.8:100. When an observation-tube 200 millimetres long is employed, every degree of rota- tion read off at 17.5° C= 0.362 maltose in 100 cubic centimetres. The reducing power of maltose is increased by treating it with dilute hydro- chloric or sulphurie acid, and it is gradually converted into dextrose. Ac- cording to Soxhlet, 1 cubie centimetre of Fehling’s solution equals 7.78 milligrammes maltose in a 1 per cent. solution, provided the former is un- diluted, and 7.4 milligrammes if it is diluted. Maltose in solution is directly fermentable by means of yeast. Dextrose is also distinguished from maltose by the fact that the former reduces Barfoed’s reagent,* whereas the latter does not. Dextrose is furthermore differentiated from maltose by the fact that the glucosazon is almost insoluble in water, whereas the malto= sazon is soluble in hot water. The following table serves to demonstrate more clearly the different products formed during the conversion of starch :— 1, Soluble Starches (Amylodextrine, Amidulin) . { fk eral Siete bag itated by tannic acid and aleohol. (mes stains it [ Precipitated in solution by al- . violet to. ma- | cohol and ether, but not with 2. Varieties | Etythrodextrine } jocany-brown | tannic acid. It does not reduce of Dextrine colour Fehling’s solution, nor does the Achroddextrine ¢ Iodine does not | addition of yeast cause fermenta- Maltodextrine { colour them — | tion. Soluble in alcohol, insoluble ( in ether, reduces Fehling’s solu- B Maltose. ee eee tion but not Barfoed’s reagent. | Yeast causes fermentation. Mal- tosazon is so'uble in hot water. Insoluble in alcohol and ether, somewhat soluble in diluted al- ee cohol; Febling’s as well as Bar- foed’s solutions are reduced. Fas- ily fermentable with yeast. Glu- cosazon is insoluble in water. * Barfoed’s reagent consists of a solution of 1 part of acetate of copper in 15 parts water to 200 cubic centimetres; to this solution, 5 cubie centimetres of acetic acid (38 per cent.) are added. 20 PHYSIOLOGY AND CHEMISTRY. Glycogen is decomposed by the salivary diastase, and likewise passes through several intermediary stages before it is converted into maltose and dextrose. If glycogen is added to filtered saliva, the brownish-red colour which results when that substance is treated with Lugol’s solution dis- appears, A reducing substance gradually develops which is at first probably maltose, and later both maltose and dextrose. The Physiologic Significance of Saliva. The first action of saliva is mechanical, and consists in covering the food-bolus with mucus, which acts as a lubricant and thus assists it in its downward passage. Therefore, swallowing is made more difficult and de- layed whenever an insufficient amount of saliva is excreted. Saliva also dis- solves easily-soluble bodies like salt, sugar, ete. The important function of starch-digestion, which is continued to a certain extent in the stomach, begins in the mouth. ‘The conversion of starch into sugar is of the highest import- ance to nutrition. Starch belongs to the class of colloidal substances which are diffused through animal membranes with difficulty. Sugar, on the other hand, belongs to the crystalloid products, which, in solution, pass through membranes with facility, and are therefore easily taken up by the blood and lymph. Finally, the: large quantities of water which are swallowed with the saliva are not without significance to the body economy. “The animal organism possesses in saliva a powerful means for the production of a continuous stream between the intestinal eanal and the blood during digestion, which carries with it the dissolved or finely divided food-produets” (Hammarsten). The Function of the Saliva in the Stomach. To judge from the rapidity of the diastatie action of saliva, one might expect the complete saccharification of the carbohydrates would oceur in a short time. That this, however, is not true may be easily determined by examination of the gastrie contents in healthy subjects after the adminis- tration of an amylaceous diet. The starches may be found present after an interval of several hours, by testing with the iodine solution for the violet colour. The action of the saliva becomes restricted by an increasing secretion of IICI, a fact which was first proven by van den Velden,2° and then by Ellenberger and Hofmeister, Ewald and mysclf.2? He demonstrated that van den Velden, Deutsches Archiv fiir klin. Medicin, 1880, Bd. 25, S. 105. 4 Ellenberger and Hofmeister, Archiv f. wissenschaftl. u. praktische ‘Thierheil- kunde, 1886, Bd. 12, S. 332, ™ Ewald and Boas, Virchow's Archiv, 1886, Bd. 104, S. 271. SALIVA. 21 small quantities of acids limited the action of the salivary diastase, and that large quantities completely destroyed it. ‘Phe following small table gives the percentages concerned, which were determined upon by Ewald and myself, and which coincide fairly accurately with the figures given by other inves gators (Hammarsten, Chittenden and Griswold, Nylén, Langley and Eves, and others) : The action of the saliva becomes ‘Restricted | Destroyed by Hydrochloric acid « 0.07% | 012% Lactic acid 0.1% 0.15 % Butyric acid . . Acetic acid. } 0.2% 04-05 fo The restriction of amylolysis is easily explained by the fact that under normal conditions the amount of hydrochloric acid equals 0.2 per cent., which may even become higher. Thus this unfavourable influence of the strong superacidity upon the process of saccharification is readily explaine whereas, on the other hand, when the diastatie activity is unrestricted, prod- uets of fermentation may develop to an excessive degree, a subject to which reference will be made later. This leads to the important question which ‘oes not seem hitherto to have received its due consideration, either from the clinical or physiologic standpoint, namely, whether an excess of acid destroys the diastatic ferment permanently or only facultatively; in other words, whether the diastase becomes active again when less acid is secreted or when it is neutralised with alkalies. I have attempted to solve this problem, and came to the conclusion that ptyaline again becomes active after alkalisation or after a decrease in the seeretion of the acid. I was able, for instance, by means of alkalisation with a soda solution, to observe a return to activity of the diastatic ferment in a starch-mixture in which the saliva had been restricted for one hour by the presence of 0.15 per cent. of HCl. It follows, therefore, that saccharifieation probably again becomes active in the later stages of gastric digestion, when the acid production is diminished. A few authors, amongst whom van den Velden?* was the first, have distinguished, on the above grounds, between two stages of digestion, namely, an amylolytic and a proteolytic. This is correct in so far that the amylaceous digestion predominates at the beginning when HCI is absent, but that the proteid digestion, which cannot dispense with free hydrochloric acid, is relatively insignificant. Nevertheless the products of proteolysis are plainly demon- strable in this stage. Aside from its diastatie action, saliva seems to have a peculiar influence % van den Velden, l. c. 22 PHYSIOLOGY AND CHEMISTRY, upon gastrie digestion, which has received especial study from Sticker? and Biernacki.” The former claims that deficient salivary activity is fol- lowed by an arrest or diminution of HCI secretion, Biernacki, who made further investigations, showed that it was not the saliva itself, but its com- bination with the food in the mouth, which favoured digestion, A. Schuld®* obtained the same results as Biernacki.